The present invention relates to a composite polymeric material comprising vinyl chloride and organosilicon moieties in combination and a method for the preparation thereof. More particularly, the invention relates to a composite polymeric material comprising vinyl chloride and organosilicon moieties in combination having a high gas permeability or, in particular, high oxygen permeability but yet free from the problem of bleeding of the plasticizer contained therein and a method for the preparation of such a composite polymeric material.
In recent years, as is well known, there is a rapidly growing demand for gas- or oxygen-permeable polymeric materials. Such a material is used, for example, in the blood transfusion or solution infusion and blood purifying unit of an artificial blood dialysis and an artificial heart-and-lung system for surgical operations including blood and solution bags and catheters, contact lenses and other medical instruments. Some of fresh foods must be stored under an atmospheric condition in a package rich in the oxygen content since otherwise the still living tissues of plants or animals of the foods rapidly decay in an atmosphere lean in the oxygen content during storage so that the material of the package should desirably be highly oxygen-permeable.
Needless to say, oxygen permeability of various polymeric materials widely differs from one to the other. For example, low-density polyethylenes reportedly have a relatively high oxygen permeability of 190 ml.mm/m.sup.2.atm.24 hours while high-density polyethylenes have an oxygen permeability of only 27 in the same unit. Polyvinylidene chloride resins are known to have a further small oxygen permeability. At any rate, the oxygen permeability of these polymeric materials is quite insufficient as an oxygen-permeable polymeric material usable, for example, for the gas or material exchange membrane for blood purification.
Polyvinyl chloride resins, on the other hand, are known to have an outstandingly high oxygen permeability when the resin is plasticized with a large amount of a plasticizer. For example, it is reported that a polyvinyl chloride resin plasticized with 55 phr (parts per 100 parts of the resin) of dioctyl phthalate plasticizer has an oxygen permeability of as high as 309 in the same unit as above. Unfortunately, such a highly plasticized polyvinyl chloride resin cannot be used in most applications due to the safety problem despite the excellent physical and chemical properties inherent to polyvinyl chloride resins. That is, the plasticizer impregnating the polyvinyl chloride resin bleeds on the surface of the resin article unavoidably contaminating the substances in contact with the plasticized polyvinyl chloride resin while plasticizers are generally toxic against living bodies as is the serious concern in recent years. Therefore, the use of a plasticized polyvinyl chloride resin in the above mentioned medical applications and as a material for food package is quite out of question. Beside the plasticized polyvinyl chloride resins, several highly oxygen-permeable polymeric materials are known in the art but none of them is sufficiently inexpensive to ensure wide application thereof in a practical use.
It is of course that the decrease in the amount of the plasticizer formulation in a polyvinyl chloride resin blend leads to the decrease in the danger of contamination with the plasticizer. This way is, however, not practical because the oxygen permeability of a plasticized polyvinyl chloride resin rapidly decreases as the amount of the plasticizer is decreased reaching, for example, an extremely low value of only 2.9 in the same unit as above in an unplasticized polyvinyl chloride resin in addition to the loss of the flexibility possessed by a polyvinyl chloride resin when it is plasticized.
Several attempts have been made, of course, to solve this problem, for example, by the use of a polymeric plasticizer having less tendency toward bleeding and migration or less toxicity or by the techniques of copolymerization of vinyl chloride with one or more comonomers having a plasticizing effect in the copolymeric resin increasing the oxygen permeability of the resin. For example, a terpolymeric resin of vinyl chloride, ethylene and vinyl acetate is sold on the market as an oxygen-permeable polymer but the oxygen permeability of one of the commercially available resins of this type is 191 in the same unit as above not to be high enough to satisfy the demand in the practicl uses. The results obtained by using a polymeric plasticizer is also not better than above.
Thus, no polymeric material is known in the prior art to meet the diversified requirements in the medical science and foodstuff industry in connection with the oxygen permeability and the problem of plasticizer bleeding.